1. Field of the Invention
This invention relates to document sorting systems and particularly to apparatus for detecting jamming of documents in document sorting tracks and to the prevention of further jamming. The system involves detecting conditions attendent to jamming in document handling tracks and taking immediate action to prevent the introduction of new documents into a track while clearing the track by routing documents to their proper pocket destinations or to a missort pocket.
2. Description of the Prior Art
Exemplary prior art apparatus for preventing jamming in document processing equipment is disclosed in U.S. Pat. no. 4,151,410 dated Apr. 24, 1979. Apparatus according to that patent employs sensors spaced along document transport tracks to monitor the passage of the documents. Typically, the sensors are used to detect the translucency of each document. Translucency is variable through a document in motion because of irregularities in the paper. If no changes in translucency are perceived for a time while the equipment is running, it is understood that the document has stopped moving and the equipment has probably jammed. Additional related prior art involving the sensing of translucency is disclosed in U.S. Pat. No. 4,160,546 which is directed to the detection of overlap between documents in a document processing apparatus. That patent shows means for detecting overlap by testing for differences in translucency. While they concern relevant art, neither of the foregoing patents is believed to illustrate art which anticipates the present invention.
A related patent application is U.S. Ser. No. 942,469, filed Sept. 14, 1978, which relates to a Constant Spacing Document Feeder. That application involves apparatus which drives a feed wheel at an average speed, dependent upon the length of a document to provide constant spacing between documents. That application clearly does not anticipate the processing system employed in the practice of the present invention.
In the prior art, such as that referred to above, sensors in the individual pockets provide signals indicating when documents are received in the pockets. These signals are used to aid in determining when there is a missort and to operate signal devices, such as lamps, indicating that a missorted document has been placed in a particular pocket.
Prior art devices such as those outlined above have functioned well in earlier models of document processing equipment, but have not been found to be satisfactory in present machines which operate at higher speeds. In addition, the provision of separate detectors and display devices for each document pocket for the purpose of determining that missorted documents are present has proven to be costly. In addition, when a jam condition occurs, a need exists with present routing to clear the machine, which includes stopping the machine feeder to prevent the entry of further documents into the track and then clearing the track. Clearing the track, as conceived for present apparatus, involves completing the sorting of documents in the track upstream and downstream of the point at which the jam occurs while diverting a minimum number of documents to a pocket designated to receive non-sorted documents. These new requirements have led to a search for better means and to the development of the present invention.